1. Field of the invention
The present invention relates to a video tape recorder and, more particularly, to an improvement of a tape loading/unloading arrangement for use in an 8 mm tape video tape recorder.
2. Description of the Prior Art
One prior art tape loading system employed in the VHS video tape recorder is known as an M-loading system, wherein a tape portion pulled out from the tape cassette is extended partially around a guide cylinder, which is provided with one or more magnetic heads. The tape is pulled out by a pair of tape guides which are first inserted into a cassette through an opening formed therein. Then, the tape guides move in the respective grooves that extend along the side of guide cylinder, thereby applying the tape portion on the guide cylinder for a predetermined angle. The M-loading system of this general type is shown, for example, in U.S. Pat. Nos. 4,115,825 and 4,452,407.
The above described M-loading system employed in an 8 mm type video tape recorder, according to the prior art, is further explained in connection with FIGS. 1, 2a, 2b, 2c and 2d below.
A pair of tape guides 4 are held in the home-position, initially. When a tape cassette 1 is properly mounted in the tape recorder, tape guides 4 are placed inside an opening 3 formed in cassette 1. Since cassette 1 is for an 8 mm tape, opening 3 is relatively small and, therefore, the radius of the curvature of grooves 5 is very small. A pair of pivotal levers V rotate to raise the portion tape off of the cassette. Then, when tape guides 4 are moved from the home-position by a suitable driving means (not shown) along the respective grooves 5, tape guide 4 catch the tape portion 2 and pull it out of the cassette. When tape guides 4 are moved to the operating-position, in which tape guides 4 are located at the upper ends (FIG. 1) of the respective guide grooves 5 and they are engaged with stoppers 7, the tape portion pulled out of the cassette is tightly held against a tilted guide cylinder 6 in a predetermined angled relationship with the axial direction of the tilted guide cylinder 6.
Referring to FIGS. 2a-2d, tape guide 4 located at the left-hand side in FIG. 1 is shown in different viewing angles, and which includes an upright post 8 and a slanted post 9 which are mounted on a slider 10. Post 8 is defined by a roller portion 13 having flanges 11 and 12 at its opposite ends and a support 14 for supporting the roller. The height of post 8 can be adjusted by turning the post 8. Then, post 8 is held in the adjusted position by tightening a screw 15. Support 14 engages a stopper 7 (FIG. 1) so as to properly locate tape guide 4 when it is moved to the end of the corresponding groove 5.
Slider 10 has a front projection 16 extending in the direction of forward movement of slider 10 and four leg projections 17a, 17b, 17c and 17d extending on the bottom face of slider 10 at four corners thereof for sliding contact with the chassis 18, indicated by a broken line in FIG. 2b. As well as support 14, front projection 16 engages stopper 7 to locate tape guide 4 when it is moved to the end of the corresponding groove 5. A pair of engagement-projections 19 and 20 extend downwardly from the bottom face of slider 10 for engagement with guide groove 5, and is connected with a driver means (not shown) which provides a moving force to guide 4.
Since the tape portion is wound on tilted guide cylinder 6, some twisting force is applied to the running tape so that the tape can not follow the original path on the tilted guide cylinder. Thus, the tape tends to change its path during the movement, resulting in unstable movement of the tape. To keep the tape following the orignal path on the tilted guide cylinder, post 9, tilted in a predetermined angle, is provided on each tape guide 4. The employment of such a slanted post 9 is disclosed in Japanese Patent Publication No. 58-27580, issued June 10, 1983 and assigned to Matsushita Electric Industrial Co., Ltd. When such a slanted post 9 is employed, stable movement of the tape can be realized after the tape is completely loaded, that is, properly wound on the tilted guide cylinder 6.
However, the employment of slanted post 9 gives rise to another problem that occurs during the loading of the tape on tilted guide cylinder 6 or during the unloading of the tape from cylinder 6, as explained below.
During the loading of the tape and particularly in the case of 8 mm tape video tape recorder, tape guide 4 moves from its home-position to the operating-position, and during which slanted post 9 engages the tape, whereby the tape is undesirably twisted by the tilted post. Thus, the tape receives a force in its widthwise direction. For example, when slanted post 9, shown in FIG. 2b, engages and pulls the tape from the cassette, the tape receives a force in the upward direction. Accordingly,the upper edge of the tape rubs against flange 11, which may cause undesirable damage to the tape. The same problem arises during the unloading of the tape, that is, when tape guide 4 moves from its operating-position to the home-position.
The above described problem is further described with reference to FIGS. 9 and 10.
According to the prior art tape loading arrangement such as shown in FIG. 9, with respect to the tape guide provided on the left-hand side, an angle .theta.L contained between a line extending between the centers of tape reels and a line containing the axis of slanted post 9 when viewed in FIG. 9, which is located at a position slightly touching the tape, is relatively large. When the angle .phi.L becomes greater, slanted post 9 contacts the tape in a more slanted manner, thereby producing a force in the widthwise direction of the tape. Such a widthwise force can be reduced by reducing the tilting angle of the tilted post itself or by reducing an angle .phi.L contained between the line containing slanted post 9 and the line representing the direction of movement of the tape guide 4. Since the tilting angle of the tilted post is determined by the angle of guide cylinder 6, the tilting angle of the post can not be changed.
An attempt has been made by one of the present inventors to change the angle .theta.L. Generally, as shown in FIG. 9, the angle .theta.L is about 90.degree., and is changed to about 80.degree., as shown in FIG. 10. Accordingly, the angle .phi.L is made smaller than that in FIG. 9.
In this respect, the above described problem of producing unwanted widthwise force may be reduced to some degree, but another problem arises if the angle .theta.L is made less than 80.degree.. That is, as the angle is made less than 80.degree., it is necessary to bring tape guide 4 closer to guide cylinder 6 so as to ensure the contact between slanted post 9 and guide cylinder 6. However, if tape guide 4 is brought too close to guide cylinder 6, the edge of the tape guide 4 may undesirably scrape the face of guide cylinder 6, resulting in damage of the magnetic head.
A similar problem may arise for the tape guide provided on the right-hand side. If so, the same rearrangements may be done to the tape guide and its associated parts, if necessary. However, if the guide grooves to the right and left of the guide cylinder are asymmetric to each other, such as shown in FIG. 9, where capstan CP is located on the right-hand side of the cylinder, the angle .phi.R is already sufficiently small. Therefore, it is not necessary to further adjust the tape guide and its associated posts.